The Mpemba Effect
The Mpemba effect is the process of warm water freezing faster than cold water. This process goes against logic and much of what we know about thermo chemistry. Though the exact cause of the Mpemba effect is unknown, it is not a newly discovered phenomenon. Aristotle made the first record of the Mpemba effect in the days of ancient Greece.1 Though the name is new, the effect itself is as old as humanity, and hopefully with new technology we will be able to discover more about the effect and its causes.
Aristotle wrote that “If water has been previously heated, this contributes to the rapidity with which it freezes: for it cools more quickly.”1 This observation mirrors what Mpemba later observed, where he saw a warmer liquid freeze faster than a cooler one. This is the first written record of what would later be known as the Mpemba effect.
Aristotle used his observations about the nature of water to develop his theory of antiperistasis. This theory refers to the “sudden increase in the intensity of a quality as a result of being surrounded by its contrary quality.”1 According to this theory being surrounded by warm water would cause something to cool rapidly, and vice-versa. Though this theory is not correct, it provided a basis for understanding the Mpemba effect that was accepted well into the 17th century.
Roger Bacon is the next to record his observations of the Mpemba effect. He wrote, “Water slightly warm is more easily frozen than quite cold.”3 This was a further development in the understanding of the Mpemba effect. The invention of the thermometer helped Bacon and many of his contemporaries understand subtleties that escaped Aristotle. This allowed him to make a more defined statement about the Mpemba effect than Aristotle had been able to. While Aristotle developed a theory to explain the Mpemba effect, Bacon wrote that it was a phenomenon that could, under some circumstances exist.1 Understanding of the Mpemba effect had increased, and the advance of modern technology would continue to allow our understanding of the effect to advance.
Erasto Mpemba made the modern discovery of the Mpemba effect at a secondary school in Tanzania in 1963. Mpemba had no scientific degrees or advanced levels of expertise when he rediscovered the effect. It was in many ways a matter of chance that he discovered the effect at all. According to the story that he later reported, Mpemba and his fellow students were making ice cream, and Mpemba put in a hot mixture of ice and milk into the freezer without waiting for it to cool. He later discovered that his mixture had frozen faster than the mixtures of the other students.1
Mpemba was shocked when he observed that his mixture had frozen first. He asked his teacher for an explanation, but his teacher dismissed Mpemba’s results, and mocked him for believing that this was even possible. Mpemba persisted though, and continued to test his theory both with water and with milk. His results continued to confirm the Mpemba effect.
Eventually Mpemba had the opportunity to question a professor at a nearby university about his discovery. Though the professor was initially shocked that a student would ask him why hot water froze faster than cold he tested Mpemba’s theory. His results confirmed the Mpemba effect, and in 1969 Dr. Osborne and Mpemba jointly published their results.
There are several factors that are believed to influence or cause the Mpemba effect. One of these causes is supercooling.3 Supercooling occurs when a liquid goes to a temperature lower than 0 degrees Celsius before it freezes. It is possible that the initially cold water could go to a colder temperature than the initially warm water before it freezes.
Though it is possible that supercooling influences the Mpemba effect, it is not the sole cause In fact, if supercooling does influence the Mpemba effect then it raises the question of “Why should initially cold water supercool more than initially hot water?”3
Another possible cause for the Mpemba is the mass of the water.1 Though both bodies of water start out with the same mass, the sample that is heated probably loses some of its mass to evaporation. This means that when they are cooling down the warmer water could in fact have a lower mass then the sample of colder water. Since the warmer water has the lower mass, it will be easier to freeze then the sample of colder water.1
One further possible cause of the Mpemba effect is dissolved gases.3 According to this explanation the dissolved gases that are usually in water are expelled when the warmer sample is heated. This leads to a change in the properties of the warmer sample of water, which can lead to a change in its freezing point. This explanation is one of the more likely ones, though experiments that have boiled both quantities of water in order to eliminate this factor have still observed the Mpemba effect.3
Almost all of the explanations for the Mpemba effect refer back to the fact that one sample of water has been heated, and that the other hasn’t. This is the logical explanation for the effect, since it is the only perceivable difference between the two samples of water. Yet there are almost too many possible factors that influence the Mpemba effect to design an experiment that could conclusively prove or disprove the effect. It is simply impossible to control enough of the variables to get conclusive results.
The importance of the Mpemba effect is debatable. Since it is so difficult to determine the causes of the effect, any applications of the effect are far off in the future. Until a effective experiment can be performed we will never know if the causes of the Mpemba effect are in fact trivial or are instead of a great importance and will help us further understand our universe.
Sources
1. Jeng, Monwhhea. Hot Water can freeze faster than cold?!?. Edwardsville, IL: Southern Illinois University, 2005.
First I placed Paradichlorobenzene in melting point capillaries. I then placed the melting point capillaries in a beaker of water that I heated to temperatures of 75, 80, 85, 90, 95 and 100 degrees Celsius. When I observed that all of the samples of Paradichlorobenzene had melted, I removed the melting point capillaries from the beaker of water. I then timed how long it took each sample of Paradichlorobenzene to return to a solid state. In each trial there were three melting point capillaries that were placed in the beaker of water.
Results
.
My results showed that there it was possible for the Mpemba effect to exist. Some of the warmer samples cooled faster than some of the cooler samples of Paradichlorobenzene. At the same time, some of the cooler samples froze faster than some of the warmer samples.
My results showed that the existence of the Mpemba effect is possible. Some of the warmer samples were observed to freeze faster than some of the cooler samples, and the Mpemba effect is a possible explanation for this. There were however, some flaws in my experiment. One of these was that I merely observed when the Paradichlorobenzene was frozen and melted, I had no scientific process in place to confirm my observations. This means that some of the freezing times could be either faster or slower than they actually took. A way to avoid this flaw would have to have had some system of measurements in place that could either confirm or debunk my observations.
Despite this flaw, I believe that my experiment was performed well. The observations and freezing times were made as accurately as possible considering the circumstances under which the experiment was performed. Though my experiment does not either entirely confirm or deny the existence of the Mpemba effect in substances other than water, it shows that the Mpemba effect may exist. It is possible that the Mpemba effect was the condition that caused some of my warmer samples to freeze faster than some of the colder ones.
References
1. Jeng, Monwhhea. Hot Water can freeze faster than cold?!?. Edwardsville, IL: Southern Illinois University, 2005.
Table of Contents
The Mpemba Effect
DavidIntroduction
The Mpemba Effect
The Mpemba effect is the process of warm water freezing faster than cold water. This process goes against logic and much of what we know about thermo chemistry. Though the exact cause of the Mpemba effect is unknown, it is not a newly discovered phenomenon. Aristotle made the first record of the Mpemba effect in the days of ancient Greece.1 Though the name is new, the effect itself is as old as humanity, and hopefully with new technology we will be able to discover more about the effect and its causes.
Aristotle wrote that “If water has been previously heated, this contributes to the rapidity with which it freezes: for it cools more quickly.”1 This observation mirrors what Mpemba later observed, where he saw a warmer liquid freeze faster than a cooler one. This is the first written record of what would later be known as the Mpemba effect.
Aristotle used his observations about the nature of water to develop his theory of antiperistasis. This theory refers to the “sudden increase in the intensity of a quality as a result of being surrounded by its contrary quality.”1 According to this theory being surrounded by warm water would cause something to cool rapidly, and vice-versa. Though this theory is not correct, it provided a basis for understanding the Mpemba effect that was accepted well into the 17th century.
Roger Bacon is the next to record his observations of the Mpemba effect. He wrote, “Water slightly warm is more easily frozen than quite cold.”3 This was a further development in the understanding of the Mpemba effect. The invention of the thermometer helped Bacon and many of his contemporaries understand subtleties that escaped Aristotle. This allowed him to make a more defined statement about the Mpemba effect than Aristotle had been able to. While Aristotle developed a theory to explain the Mpemba effect, Bacon wrote that it was a phenomenon that could, under some circumstances exist.1 Understanding of the Mpemba effect had increased, and the advance of modern technology would continue to allow our understanding of the effect to advance.
Erasto Mpemba made the modern discovery of the Mpemba effect at a secondary school in Tanzania in 1963. Mpemba had no scientific degrees or advanced levels of expertise when he rediscovered the effect. It was in many ways a matter of chance that he discovered the effect at all. According to the story that he later reported, Mpemba and his fellow students were making ice cream, and Mpemba put in a hot mixture of ice and milk into the freezer without waiting for it to cool. He later discovered that his mixture had frozen faster than the mixtures of the other students.1
Mpemba was shocked when he observed that his mixture had frozen first. He asked his teacher for an explanation, but his teacher dismissed Mpemba’s results, and mocked him for believing that this was even possible. Mpemba persisted though, and continued to test his theory both with water and with milk. His results continued to confirm the Mpemba effect.
Eventually Mpemba had the opportunity to question a professor at a nearby university about his discovery. Though the professor was initially shocked that a student would ask him why hot water froze faster than cold he tested Mpemba’s theory. His results confirmed the Mpemba effect, and in 1969 Dr. Osborne and Mpemba jointly published their results.
There are several factors that are believed to influence or cause the Mpemba effect. One of these causes is supercooling.3 Supercooling occurs when a liquid goes to a temperature lower than 0 degrees Celsius before it freezes. It is possible that the initially cold water could go to a colder temperature than the initially warm water before it freezes.
Though it is possible that supercooling influences the Mpemba effect, it is not the sole cause In fact, if supercooling does influence the Mpemba effect then it raises the question of “Why should initially cold water supercool more than initially hot water?”3
Another possible cause for the Mpemba is the mass of the water.1 Though both bodies of water start out with the same mass, the sample that is heated probably loses some of its mass to evaporation. This means that when they are cooling down the warmer water could in fact have a lower mass then the sample of colder water. Since the warmer water has the lower mass, it will be easier to freeze then the sample of colder water.1
One further possible cause of the Mpemba effect is dissolved gases.3 According to this explanation the dissolved gases that are usually in water are expelled when the warmer sample is heated. This leads to a change in the properties of the warmer sample of water, which can lead to a change in its freezing point. This explanation is one of the more likely ones, though experiments that have boiled both quantities of water in order to eliminate this factor have still observed the Mpemba effect.3
Almost all of the explanations for the Mpemba effect refer back to the fact that one sample of water has been heated, and that the other hasn’t. This is the logical explanation for the effect, since it is the only perceivable difference between the two samples of water. Yet there are almost too many possible factors that influence the Mpemba effect to design an experiment that could conclusively prove or disprove the effect. It is simply impossible to control enough of the variables to get conclusive results.
The importance of the Mpemba effect is debatable. Since it is so difficult to determine the causes of the effect, any applications of the effect are far off in the future. Until a effective experiment can be performed we will never know if the causes of the Mpemba effect are in fact trivial or are instead of a great importance and will help us further understand our universe.
Sources
1. Jeng, Monwhhea. Hot Water can freeze faster than cold?!?. Edwardsville, IL: Southern Illinois University, 2005.
2. Jeng, Monwhea. "Can hot water freeze faster than cold?". University of California. March 16, 2010 <http://www.physics.adelaide.edu.au/~dkoks/Faq/General/hot_water.html>.
3. Sanders, Laura. "It's True: Hot Water Really Can Freeze Faster than Cold". Wired Magazine. March 14, 2010 <http://www.wired.com/wiredscience/2010/03/icy-hot/?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+wiredscience+%28Blog+-+Wired+Science%29&utm_content=Google+Reader>.
Procedure
First I placed Paradichlorobenzene in melting point capillaries. I then placed the melting point capillaries in a beaker of water that I heated to temperatures of 75, 80, 85, 90, 95 and 100 degrees Celsius. When I observed that all of the samples of Paradichlorobenzene had melted, I removed the melting point capillaries from the beaker of water. I then timed how long it took each sample of Paradichlorobenzene to return to a solid state. In each trial there were three melting point capillaries that were placed in the beaker of water.Results
.My results showed that there it was possible for the Mpemba effect to exist. Some of the warmer samples cooled faster than some of the cooler samples of Paradichlorobenzene. At the same time, some of the cooler samples froze faster than some of the warmer samples.
Temperature (Degrees Celsius.) Freezing Time (Seconds)
75 77
75 7675 8280 88
80 93
80 77
85 90
85 80
85 85
90 87
90 95
90 88
95 105
95 99
95 103
100 110
100 112
100 114
Conclusions
My results showed that the existence of the Mpemba effect is possible. Some of the warmer samples were observed to freeze faster than some of the cooler samples, and the Mpemba effect is a possible explanation for this. There were however, some flaws in my experiment. One of these was that I merely observed when the Paradichlorobenzene was frozen and melted, I had no scientific process in place to confirm my observations. This means that some of the freezing times could be either faster or slower than they actually took. A way to avoid this flaw would have to have had some system of measurements in place that could either confirm or debunk my observations.
Despite this flaw, I believe that my experiment was performed well. The observations and freezing times were made as accurately as possible considering the circumstances under which the experiment was performed. Though my experiment does not either entirely confirm or deny the existence of the Mpemba effect in substances other than water, it shows that the Mpemba effect may exist. It is possible that the Mpemba effect was the condition that caused some of my warmer samples to freeze faster than some of the colder ones.
References
1. Jeng, Monwhhea. Hot Water can freeze faster than cold?!?. Edwardsville, IL: Southern Illinois University, 2005.
2. Jeng, Monwhea. "Can hot water freeze faster than cold?". University of California. March 16, 2010 <http://www.physics.adelaide.edu.au/~dkoks/Faq/General/hot_water.html >.
3. Sanders, Laura. "It's True: Hot Water Really Can Freeze Faster than Cold". Wired Magazine. March 14, 2010 <http://www.wired.com/wiredscience/2010/03/icy-hot/?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+wiredscience+%28Blog+-+Wired+Science%29&utm_content=Google+Reade r>.